weird problem - on Sunday I downloaded and upgraded my system.
Using synaptic - when the upgrade was done, some 16 packages all
failed with MD5 errors AND when I quit synaptic, the system was
completely bust. Would not even reboot.

So I reinstalled a fresh copy, set what I needed and redid the upgrades,
this time from a different mirror.
Boom - same problem with the MD5 errors and again the system is bust.
Redid a fresh install on my dev box, downloaded and installed the upgrades
and ditto - exactly the same problem.
Cannot even logout properly, network is down etc.etc.

So I'll have to rebuild the systems again.
Anybody ever had something like this happen?

Let me see if I have this straight. You upgraded your system to Fedora 9 from CD and everything was fine but then you used synaptic to update it later and this problem occurred. Is this correct? Are you only updating from the Fedora 9 repositories or are you using 3rd party repositories. I assume you have verified that you were using Fedora 9 and not older versions of the repositories. Have you tried to update with yum?

yep - in short that is what happened
only it was not an upgrade but a fresh install
AND the 2nd time the machine actually booted but the X-server
wont start - used alt-ctrl-F1 to get to a login screen
(this took about 5 minutes!)

rebuilt the machine again and then used yum to do
the updates (3rd time)
checked the updates I kept from the previous install
against the newly downloaded files and they were the same
AND again the X-server only seems bust
the machine boots and I can get to a login screen as above
but it hangs when trying to use "startx" without any error messages
or any indication of what is wrong
yum had similiar errors re. the MD5 on the same set of files
It seems it updated parts - then stopped the remainder of the updates due to the MD5 errors
Starnge (sic)

As soon as I get time I'll try to install again
then using synaptic - exclude the files with the MD5 errors
and see what happens - this might then by default not try and update
some other files due to dependencies

I didn't even know synaptic was included in Fedora 9. That is some odd behavior for sure. I have never done a fresh install of 9, only one upgrade so far and that went smoothly. Are you sure the disks are good? Did you do a verify on them? If you are getting checksum errors it sounds like there is a problem with the disk burn.